They are identical twins, and as is so often the case, you may have to ask their parents how to tell them apart.

Oasis of the Seas has the Seafood Shack; Allure of the Seas has Rita's Cantina. Allure features performances of Chicago: The Musical; Oasis has Hairspray. Allure's captain claims his ship is nearly two inches longer than Oasis, which for the last year has carried the banner of world's largest cruise ship. There are about half a dozen other differences, but on the scale of these massive ships, they are the equivalent of small birthmarks.

What really distinguishes Allure -- which will embark on its inaugural Caribbean cruise from Port Everglades Sunday evening -- is that it is the first ship to carry DreamWorks Animation characters including Shrek, Po from Kung-Fu Panda and Madagascar's penguins, positioning Royal Caribbean to compete more aggressively with Disney and Norwegian cruise lines for family business.

"We think this will appeal across the board to adults and children," said Adam Goldstein, president and CEO of Royal Caribbean International.

Royal Caribbean has long promoted its ships as family-friendly, but putting DreamWorks characters in parades, shows and character breakfasts allows it to go head-to-head with Disney, which pioneered such activities, and Norwegian, which has Nickelodeon characters on two of its ships. Oasis and two other Royal Caribbean ships will get the DreamWorks characters between now and April, but the cruise line held off on putting the characters on those ships until they could be introduced on Allure.

Company officials are calling Allure "the entertainment ship," taking a page from Norwegian's Epic, which debuted this summer boasting of its many entertainment options. A musical parade on Allure's Royal Promenade features DreamWorks characters and is reminiscent of -- although not as large or complicated as -- a parade at a Disney theme park. And in press kits handed to members of the media on a preview cruise was a headband with a pair of ears -- only these were green, like Shrek's.

To someone who has cruised on Oasis, Allure will feel familiar. The differences are not architectural but are in how the space is used.

Living large

Allure's vital statistics are the same as those of Oasis. The ship is 1,187 feet long, 215 feet wide, stands 213 feet above the water line, has 16 passenger decks, and carries 5,400 guests at double occupancy (6,318 if every berth is filled). It is an enormous ship.

Allure is 37 percent bigger than Royal Caribbean's Freedom-class ships, based on gross tonnage, with much of the increase in the ship's width. It is that width that accommodates Central Park and the inside staterooms that have balconies overlooking the park; the Boardwalk, with the AquaTheater and carousel; and the Royal Promenade, which houses shops and restaurants and the DreamWorks parade -- features that make the Oasis-class ships unique.

The novelty of the two huge ships, as well as their amenities, are commanding high prices. Of the 16 ships sailing week-long cruises of the eastern Caribbean in March from Miami, Fort Lauderdale and Port Canaveral, Oasis has the highest fare on Cruises.com: $1,265 per person double occupancy for the cheapest inside cabin. Allure is next highest at $1,149, followed by the Disney Magic at $1,089. Even Celebrity, Royal Caribbean's usually pricier sister company, costs less -- $759-$859, depending on the ship. All the others start at less than $700.

"In South Florida, since we know Royal Caribbean so well, people love Royal Caribbean," said Mary Beth Casey, owner of Expedia CruiseShipCenters, a Weston travel agency.

"DreamWorks puts them in direct competition with Norwegian, but the point of view our clients have is 1 / 8the Oasis-class ships are 3 / 8 a notch above," she said. "The Disney product is excellent, it's unique in its own way, but Oasis and Allure are going to give them a lot of competition."

When Royal Caribbean introduced Oasis of the Seas a year ago, Goldstein said, many people asked if a ship so large would work and whether it would sell. "Both ships are doing phenomenonally well," he said, and no one is asking those questions anymore.

Why are people willing to pay a premium to sail on Oasis and Allure?

"There is a sense of people wanting to be on the newest ship," said Casey. "Some of that is wanting the experience, some of it is being able to brag about it. And here in South Florida, it's just easier to understand what's special and different. I think it's the totality of the full uniqueness of it."

The uniqueness of the Oasis-class ships is largely in its seven "neighborhoods," especially Central Park, the Boardwalk and the Royal Promenade, but also Entertainment Place, with the main theater, casino, ice rink and several clubs; the Pool & Sports Zone, with two surf pools, Zip Line, and other recreational facilities; the Vitality at Sea Spa and Fitness Center; and the Youth Zone, with arcades, lounges, art and science labs and other kids programs, divided by age groups.

Special effects

Royal Caribbean has tweaked those zones to give Allure its own personality. Among the differences:

--Characters from four DreamWorks films -- Shrek, Kung Fu Panda, Madagascar and How to Train Your Dragon -- star in the AquaTheater production Let You Entertain Me, the DreamWorks parade, the How to Train Your Dragon ice skating show, and character breakfasts. Allure also has 3-D screens in the Amber Theater, where guests can watch first-run DreamWorks movies. These features will be added to three other Royal Caribbean ships.

--Allure has a Starbucks on the Royal Promenade, the first on a cruise ship. Coffee drinks and a limited selection of food items are available for the same price you'd pay at your neighborhood Starbucks.

--At night, the Solarium Bistro, which serves spa food for breakfast and lunch, turns into the Samba Grill, an extra-fee Brazilian churrascaria featuring grilled meat and seafood brought to the table on skewers and sliced for each diner, as well as an extensive antipasto and salad bar. On an early preview cruise for the media and travel agents, eight varieties of meat were served.

"We found our guests love eating healthy for breakfast and lunch, not so much for dinner," said Lisa Bauer, Royal Caribbean's senior vice president for hotel operations. Cost: $25; for vegetarians, there's a $15 charge for the salad bar.

--Rita's Cantina, a casual extra-fee restaurant featuring Mexican food, replaces the Seafood Shack on the Boardwalk. Food and service got mixed reviews on the preview cruise. "Cigars" -- like small, cylindrical deep-fried tacos -- were greasy and the fried taste overwhelmed the flavor of the filling, but a ceviche tostada with small shrimp was light and tasty. Tables sat empty, waiting to be cleared, for long periods, while people in line were told the wait would be an hour or longer. Cost: $7.95.

--The Boardwalk Dog House serves sausages, wieners and brats, at no extra charge. The Dog House is in the space that on Oasis is occupied by Boardwalk Donuts, which moves next to the ice cream parlor.

--Central Park has a gallery of works by Romero Britto, the contemporary pop artist's first gallery at sea. Britto also created a butterfly sculpture for Central Park's gardens and a teddy bear available only on the ship. Prices are slightly higher than those on land -- but without tax.

--The Royal Promenade has a Guess accessories boutique, the first at sea.

--Shows unique to Allure are Chicago: The Musical; an elaborate song, dance and acrobatics production called Blue Planet; and OceanAria, an aquatic and high-dive show in the AquaTheater.

--Staterooms have iPod docking stations with clocks. In addition, in response to customer complaints, Allure has added a triple electrical outlet on top of the desk (the outlets on Oasis are under the desk and hard to get to) and put more toiletries in the cabins. Those changes are planned for Oasis as well.

"The lessons we learned from Oasis made up a 77-page document," Bauer said. "Most of the comments we got about things that needed to be tweaked were in the staterooms. The No. 1 request we got was a clock."

The Royal Caribbean Quantum of the Seas was built at the Meyer Werft shipyards and delivered in October 2014. It's the first of two ships that have been part of the line's Project Sunshine. The sister ship Anthem of the Seas is due in spring 2015. Read about ship details